Types of ophthalmologic apparatuses include ophthalmologic imaging apparatuses for obtaining images of an eye and ophthalmologic measuring apparatuses for measuring characteristics of an eye.
Examples of ophthalmologic imaging apparatuses include an optical coherence tomography (OCT) apparatus that obtains cross sectional images using OCT, a retinal camera that photographs a fundus, a Scanning Laser Ophthalmoscope (SLO) that obtains images of a fundus by laser scanning with a confocal optical system, a slit lamp that obtains images by photographing an optical section of a cornea using slit light, etc.
Moreover, examples of ophthalmologic measuring apparatuses include an eye refractivity examination apparatus (refractometer, keratometer) that measures refractive properties of an eye, a tonometer, a specular microscope that obtains properties of a cornea (cornea thickness, cellular distribution, etc.), a wave-front analyzer that obtains aberration information of an eye using a Shack-Hartmann sensor, etc.
Regarding ophthalmic examinations using these apparatuses, in terms of precision and accuracy of examinations, position matching between the optical system of the apparatus and an eye is very important. This position matching includes alignment and tracking. Alignment includes the action of aligning the light axis of the optical system of the apparatus with respect to the axis of an eye (xy alignment), as well as the action of adjusting the distance between the eye and the optical system of the apparatus (z alignment). Tracking is an action of detecting the movement of an eye and changing the position of the optical system of the apparatus in accordance with the eye.